This example is Markdown, but you can insert an image tag in a Textile
page too (and, of course, a Haml page). That's one of the nice things
about Markdown and Textile; if they don't support what you need you can
drop into HTML to say what you really mean. I find that it's rarely
necessary, but it's nice to be able to fall back on HTML if the need
arises.

There's nothing to stop you from putting your images into Nesta's
public directory (any file that you drop into public will be served
automatically). The only reason that the content/attachments directory
exists is that it allows you to keep your text and images together
inside the content folder.